The present invention relates generally to the sleeper sofa field and, more particularly, to a sleeper sofa mattress providing both increased sitting and sleeping comfort over an extended service life.
Sleeper sofas are well known in the art. A sleeper sofa generally includes a sofa frame and a folding mattress frame and cooperating mattress. A sleeper sofa may be used as a bed by unfolding the mattress frame so as to extend horizontally from the sofa frame. When opened, the mattress rests on and is supported by the extended mattress frame for sleeping. The sleeper sofa may also be used as a conventional sofa by folding the mattress frame and mattress and then sliding them into the sofa frame. Seat cushions are placed on the sofa frame overlying the folded mattress and mattress frame for both improved aesthetics and sitting comfort.
While sleeper sofas have been available for a number of years, certain design problems have not been solved satisfactorily to date. Specifically, since the mattress frame must be able to support at least one and possibly two individuals when extended to form a bed, it must be solid and sturdy. Because of space limitations within the confines of the sofa frame and the requirement of folding capability, possible structural arrangements of the mattress frame components are somewhat limited. As a result, manufacturers have almost universally adopted the use of one or more cross bars extending transversely across the frame to provide the desired rigidity and support.
This solution to the rigidity and support problem unfortunately leads to an additional comfort problem. Specifically, the sleeper sofa mattress must be designed not only to provide firm support for maximum sleeping comfort, but also to prevent the feel of the cross bars through the mattress. Solid foam mattresses are simply incapable of providing the necessary support.
In attempting to reach a solution to the support problem, there are certain design limitations that must be considered and actually conflict with achieving these desired goals. Specifically, like the mattress frame the mattress cannot be bulky since there is only limited space in the sofa frame into which the mattress must fit when the sleeper sofa is closed for sitting. Further, the mattress must be capable of being folded with the mattress frame. Thus, the mattress must allow folding along "hinge lines" extending across the mattress. These factors limit the choice of mattress materials and the design of the mattress that could otherwise increase comfort.
In recent years, a coil spring assembly has been incorporated into a head section of a foam sleeper sofa mattress in order to provide the desired support. While the coil spring assembly does supply added support particularly in the torso region, it is not foldable and, therefore, may only be positioned in the foam mattress between the hinge lines that allow folding.
A problem occurs with this type of design as when the mattress is folded, the foam material tends to separate and pull away from the coil spring assembly. Over time, wear from folding causes the splitting and erosion of the foam mattress materials, particularly along the interface with the spring assembly. Initially, this results in reduced supporting capability. Thus, for example, when sleeping on the mattress the mattress frame cross bar or even the spring assembly itself may be felt pressing uncomfortably through the mattress into the lower back region. As additional time passes, the foam mattress material may actually pull apart from the spring assembly. This results in pronounced and permanent contour irregularities of the mattress surface. In turn, this inevitably leads to having to replace the mattress.
One prior art design that addresses the problem of foam separation from a spring assembly may be r found by reviewing the disclosure of U.S. Pat. No. 4,004,305 to Rubin. In Rubin, the mattress is formed in two sections. Each section includes coil springs supported on a bottom mat and a foam cushion extending upwardly from the mat surrounding the springs. The coil springs increase the support provided by the mattress and, therefore, the sleeping comfort. The service life during which this increased comfort is provided is, however, limited.
As shown in Rubin, the two sections are joined at a hinge line by a simple fabric flap hinge. Not only is support in this area inadequate to start, but it rapidly deteriorates over time. Specifically, with nothing to hold the two sections together at the bottom the repeated folding and unfolding of the mattress causes the bottom margins of the sections to begin to pull apart and separate. This results in the coil springs within the mattress to shift and become oriented at a slight angle to the vertical when loaded. In this position the coil springs fail to provide support as originally designed. Over time, this angular orientation leads to permanent damage through the erosion of the foam cushion adjacent the coil springs and the formation of lumps or contour irregularities in the foam. As a result, it is difficult to find a comfortable position when sleeping on the mattress. Not only can this lead to a substantially sleepless night, but to aches, such as lower back pain, the next morning. Thus, a need is clearly identified for a sleeper sofa mattress capable of providing increased sleeping comfort over a longer service life.